Prompt: Deep Castle
Afore the lush forested expanses of the unexplored continental west had ever been mapped out by Equestrian conquistadors it had supposedly been home to native civilizations of ponies with fantastical powers. This discovery was a significant one in throughly understanding a more complete picture of the long history of Equestria. These ponies were unicorn mages, unrivaled in many regards, who were brilliant philosophers, architects and mathematicians. The unicorns worshiped the celestial bodies in the sky just as countless ponies had before them and just as many countless more would after. Their interpretation of the sun and moon’s importance represented a symbolic juxtaposition between two particular factions within this civilization.
The Order of Sol, snow white robed diurnal arcanists, were kindly and bubbly unicorns who worked hard during the day, planning expansions of their grand keeps and castles which had been spread all throughout the west.
Then of course there was the Order of Lun, with robes as deep blue as the midnight sky, quiet and watchful nocturnal guardians who protected the Order of Sol as they slept through the night.
Despite these ponies’ differences, there was harmony. They enjoyed a symbiotic relationship with one another, whereas they never intermingled and frequently went months without ever speaking, and yet they admired and respected one another for their essential contributions to their society. They each viewed the day and the night with equal regard. The sun offered safety, warmth and light, allowing for the day’s work to be done. The moon offered quiet, comfort and darkness, allowing for the weary workers of the day to rest.
Within the deepest, lushest of jungles stood upright and tall and expansive castle, whose foundation and walls were laid with dark stony bricks. And yet despite this ancient civilization being gone for centuries, within the castle, an aura of disharmony reigned free.
—
“A…friendship problem?” Princess Celestia asked, bewildered as she stared at the map in Twilight’s castle. “For Luna and I?”
She had arrived mere moments ago in disbelief. In many ways she didn’t think friendship problems were…well, her problem. Not to mention, her and her sister had been the subject of a friendship problem not all that long ago! At least it didn’t feel all that long ago. Far be it from her to question the Cutie Map, though, as it had sincerely helped countless ponies in the most unexpected of ways.
“I cannot imagine what friendship problem could possibly exist in the explored west…” Luna said, standing next to her taller and brighter sister.

Twilight lifted a hoof, the alicorn bursting with excitement.
“I know! Isn’t it amazing?!”
The simple prospect of going off on an adventure somewhere that was still so unknown to the world was exciting as ever to the most recently appointed princess.
“The Princesses of Equestria - summoned by the cutie map! It’s unbelievable, it’s unheard of!”
Princess Celestia exchanged an unsure glance with her sister before offering up a nervous smile to her old student.
“Ah…yes, of course, Twilight, it certainly is rather amazing. It’s just that…we’ve never…” Princess Celestia trailed off.
“We are not friendship problem solvers.” Luna was always the more blunt of the two.
“Maybe not, but neither were the others when the map sent them!” Twilight reminded. “It’s perfectly normal to have some anxiety about a friendship problem. But you two have also been through a friendship problem of your very own! I think that makes you more than qualified to help someone else with theirs!”
The obvious question which hadn’t yet been addressed, however, was the question of who. Who could possibly be having a friendship problem all the way out there? Could it have been something so simple as two explorers who disagreed on which way to go? Likely not, but it was the only possibility anyone could think of in the moment.
Uncertainty continued to swirl around the two Princesses. Regardless, they had a job to do, and they would just have to figure it out as they went…
After all, such was how everyone else solved friendship problems, right?
—
The unexplored west was lush, with forestation stretching as far as the eye could see. The cloudless sunset sky was a magnificent backdrop to a grand castle set in a clearing where the arcanists once lived. Luna and Celestia had together descended into the clearing, attempting to find the most agreeable time that day during which they would both be awake enough to handle matters of friendship. As they set their hooves on the ground, the scale of the castle truly became apparent to them. It was massive, and for an old ruins, it was surprisingly sturdily intact.
Celestia’s gaze swept across the scene before them.
“…To see such ruins in person,” she commented. “Truly a…magnificent sight!”
She began to look around, trying to immediately ascertain any possible source of the supposed friendship problem. Luna did the same. The quietness of the forest did not immediately make apparent any squabbling explorers - just an eerie peacefulness with the daytime birdsongs coming to a gradual close as afternoon shifted to evening.
“Where in a place like this could a friendship problem even happen?” Asked Celestia, understandably confused.
“I am unsure,” said Luna. “But this is where the map sent us. We must investigate. Perhaps we will find the answer we are seeking within the castle itself.”
Celestia once more took in the view of the castle. It truly was a sight to behold.
“You may be right…” Celestia agreed after a moment of consideration. “I will lead the way.”
With no objections from her sister, Celestia took the lead, beginning forward towards the ancient structure.
Such a castle that could stand the test of time was impressive in its own right. But upon entering, it would become apparent that it was even more impressive on the inside. Celestia had lit up the interior with a sunny magical aura, and the two sisters could see that despite its age, the integrity of the castle’s interior was not only intact, but it still featured remnants of the age in which it was built. There were statues which were built in the image of the sun and the moon - including interpretations of their personifications which vaguely represented Luna and Celestia, each holding up their respective celestial body. The air was heavy with a certain humidity and tasted just subtly of a rainy day.
“…It’s amazing,” Celestia had said, peering at the statues in particular. “…Are those supposed to be…of us?”
“It seems not. Not exactly, at least…” Luna said. “They do not appear exactly as we do. Instead, they are more…generic ideas of how the sun and the moon would look as if they were ponies, I believe. If we had never known about this civilization, then they likely did not know of us either.”
Celestia took those words into consideration. Was it possible that Luna was wrong? That these ponies did know of the princesses, but not the other way around? That Celestia had subjects all those years ago she did not even know existed?
It was a strange thought to be sure.
Before that thought could be entertained further, there was a crash coming from the corridor between the two statues. Celestia and Luna both jumped, startled.
“What was…?” Celestia began.
Another crash. The two exchanged glances, before each decided to bravely trot forward to investigate…

It was a remnant of ancient history. An age old argument still raging on. Something that no one would be able to believe if they had not seen it with their own eyes.
Two ghostly figures stood in the corridor of the winding castle, one in much brighter attire, the other in darker attire.
“I have told you time and time again, Cobalt, that it is the Order of Lun who led to our demise!” The brighter robed stallion exclaimed to the darker robed one. “Simply because you all refused to be normal and stand at the ready to defend your home both in the day and the night!”
“…Solanis, I plead you understand this from my perspective. That neither order should be held responsible for what has happened to us…” the other spoke much softer, and was less animated than his counterpart. Neither pony was very large - they were a smaller people, it seemed, and the two resembled each other quite glaringly.
After the initial shock of witnessing spirits, Celestia turned to look at her sister.
“Brothers, perhaps?” She contemplated.
“It seems so…” Luna said. “…Now we know why the map sent us. It is quite self explanatory…but how are we to help spirits, mere memories of a long and distant past…?”
The two didn’t hear the sisters. Instead, they turned, walking off down the hallway, continuing to argue.
Celestia reached out with a hoof, calling out to them.
“Wait!”
They wouldn’t hear her. It seemed that the two siblings were not even aware of the sisters’ presence.
Lowering her hoof, Celestia let out a soft sigh.
“…Certainly a good question, sister,” she said. The Princess of the Sun stepped forward without hesitation, wanting to investigate further.
Deep within the recesses of the castle was where they found themselves. Corridors led to spiraling stairs that led down a massive rotunda. As they walked, torches lit with white flames ignited on either side of them. The castle was thorough and dug deep under the earth.
The two ghostly figures would reappear at certain points during the descent down the stairway.
“For as long as we have lived, your order has slept through the day - during the light! You merely basked in what we have built, without ever offering anything of your own!” The one named Solanis argued.
“But we have contributed much, Solanis, you simply have not seen it with your own eyes - for it is you who sleeps during the night. Yet you blame us not for any real shortcoming, but because you require someone to blame for what has befallen us…” Cobalt said. “…It is deep within this castle that we will find solace. It is this which my Order has constructed in hopes of creating a place of shelter for this very eventuality…”
Luna and Celestia listened intently as they continued to follow the ghostly pair down the stairway. To them, it was all too familiar. Each one of them felt their heart sink as shades of their own past lifted to the surface of their thoughts.
The compassion that Luna and Celestia felt for one another was stronger than ever. They had been through this before - not only during the most consequential of their arguments regarding the cycle between day and night, but in moments too when they had the slightest of disagreements about the time of day which they were each tied to.
There were others like them in the past. And it tugged at their heartstrings in a lot of ways. Luna did not even know of these people, of the Order of Lun, who she most certainly could have confided in, who she could have guided and helped along. And Celestia felt an all too familiar guilt rise up within her. She knew that was likely what her sister was thinking - but this time she would not make the mistake of dismissing her dear little sister’s thoughts or feelings on the matter.
At the bottom of the stairway lie what appeared to be a massive and incredible shelter, deep under the earth, where an entire underground city bathed in eternal darkness crumbled into irreparable ruins. Celestia and Luna beheld the city with disbelief. The two ghostly figures stood there, beholding it as well - only for them, it was not the first time they had laid eyes on what little remained of the place they once called home.
“…Because of you all,” Solanis gestured to the city. “…We were forced to rebuild everything under the castle. And look at what that has brought us…” he spitefully grumbled. “Eternal ruin.”
Celestia put her hoof to her heart and let out a deep sigh. “No,” she muttered. “…It is not their fault…”
She shook her head.
“…It is not the nighttime’s fault!”
Luna looked up to her sister, a slight surprise in her eyes. She felt it, the love for her sister in those words. To Luna, it was proof that Celestia did truly love her, that she had learned over the years, that she had come to truly respect the night…
Luna looked forward.
She did not know what it would take to solve a friendship problem between two spirits that couldn’t even hear them, but Celestia’s determination to fight to right this wrong being cast unto the nighttime ponies inspired her as well.
The two truly were the right mares for this job.